Pedialyte, electrolyte replacement drink with reduced sugar. Made for children and adults who are in a condition where they are stressed, especially by heat.
If your cardiac health is impaired, especially if you have Congestive Heart Failure (as I do), over hydration is a real concern. When I had my heart attack back in May 2017, it was caused by excessive hydration. I had been doing volunteer work cleaning up the town cemetery, and it was hot, like it is today (92 99 101 currently). The impaired heart cannot move the increased volume of fluid in the body.
It can become further complicated by kidney failure (which, so far, I don't have...). So if your urine is clear, you already have enough hydration. Two months earlier (in Phoenix) I had become stressed during a rifle match and decided to listen to my body, which was telling me that as important as the match was, my health was not up to the challenge, and I retired from the match after the first of three relays.
That level headed decision probably saved my life that day, and allowed me to have my MI episode in a time and place where excellent health care was able to reach me in minutes.
After the hydration, do things to reduce the heat's impact.
Evaporation. Wear cotton, bring a spray bottle and lots of plain tap water to keep it filled over and over. Keeping your clothing damp (not soaked) will allow air currents to remove heat from your body by evaporation. As relative humidity increases, evaporative cooling becomes less and less effective. This added process spares much of the body's own fluids and electrolytes, going pretty far toward staving off heat exhaustion.
Think. If you're hydrated effectively (clear urine), are already doing the evaporation thing, and have a hat on with broad brim and a large air volume over the head, and you're still uncomfortable enough that it intrudes into your shooting concentration, A) you've already last the match, and B) you may be threatening your life, too. Heat exhaustion kills.
So think, too. If you have impaired cardiac health, and especially of you have kidney failure issues, seriously consider rescheduling activities that can threaten your future.
Greg
PS My Wife Celia is in the hospital right now with a serious heat injury. She was in Phoenix a week back and tripped in the hotel parking lot, which was paved with blacktop. The temp was 114. The pavement was so hot she couldn't touch it to push herself back up. It took over ten minutes before a passerby found her and was able to help her up. When she checked herself into Emergency, she had second degree burns on a significant portion of her lower body, complicated by bad abrasions. She had one surgical procedure Monday to clear the healing skin, and is due for another one tomorrow. She may come home over the weekend, but more likely Monday.
She's a tough cookie, but this one has us all rattled. She is in University Hospital, Banner, in Tucson and receiving the highest level of great care. Elena is staying in town with her while I tend the home and the four critters 80 miles East of there.
We're doing as well as is possible, but again, I say to you guys, when the heat gets up there, think ahead; what happened to her could happen to anyone. I'm 72 and far from tiptop shape. There's a heat advisory this week. I'm staying home in the A/C, we already have more than enough excitement going on at the moment without me making bad decisions on top of all that.